Fix IMMS debug shell command

It turns out the previous CL [1] introduced a new option not as
  adb shell cmd input_method refresh_debug_properties
but as a sub command of
  adb shell cmd input_method ime refresh_debug_properties
or
  adb shell ime refresh_debug_properties

This is not what we intended.

With this CL, 'refresh_debug_properties' is recognized as a sub
command of 'adb shell cmd input_method' as we intended.

 [1]: Ibf9dab3d9c138b5f04e053d41ee4fd248c78e4da
      75a92392

Bug: 37617707
Test: Verify following command reverts the behavior to the
      previous one:
        adb root
        adb shell setprop debug.optimize_startinput false
        adb shell cmd input_method refresh_debug_properties
Test: The following command is not recognized.
        adb shell ime refresh_debug_properties
Change-Id: I89b0900f402940d5943e1a6c6e236592b5cefc78